Radio link synchronization in a wireless communication device

ABSTRACT

A wireless communication terminal including a controller coupled to a transceiver wherein the controller is configured to determine a synchronization based on a mapping of channel state information to decoder error rate corresponding to a hypothetical control code word, to attempt to decode a control codeword in a received signal, and to conclude that an out of synchronization event has not occurred if the control codeword is decoded successfully regardless of an indication of the mapping.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. application No. 61/112,482filed on 7 Nov. 2008, the contents of which are hereby incorporated byreference and from which benefits are claimed under 35 U.S.C. 119.

FIELD OF THE DISCLOSURE

The present invention relates to wireless communications and moreparticularly to determining synchronization of a radio link in awireless communication terminal.

BACKGROUND

The Third Generation Partnership Project (3GPP) is developing a LongTerm Evolution (LTE) carrier using a physical layer based on globallyapplicable evolved universal terrestrial radio access (E-UTRA). A mobileterminal or station (MS), also referred to as User equipment (UE), mayuse a cell-specific reference signal as a metric to determine if a radiolink with the base station is in synchronization or out ofsynchronization by determining whether reliable transmission of aphysical downlink control channel (PDCCH) code word with specificformats can be supported over the link.

The various aspects, features and advantages of the disclosure willbecome more fully apparent to those having ordinary skill in the artupon careful consideration of the following Detailed Description thereofwith the accompanying drawings described below. The drawings may havebeen simplified for clarity and are not necessarily drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a communication system.

FIG. 2 illustrates a possible configuration of a computing system to actas a base station.

FIG. 3 illustrates in a UE block diagram.

FIG. 4 is a flowchart for determining a synchronization event.

FIG. 5 is a flowchart for determining whether a radio link is out ofsynchronization.

FIG. 6 is a flowchart for determining whether a radio link is insynchronization.

FIG. 7 illustrates a receiver transitioning from DRX mode to non-DRXmode.

FIG. 8 illustrates a receiver transitioning from a first DRX mode to asecond DRX mode.

DETAILED DESCRIPTION

A method, telecommunication apparatus, and electronic device fordetecting a status of a radio link are disclosed. A transceiver maymaintain a radio link with a network base station. A processor may mapchannel state information to a synchronization status associated withthe radio link based on the received signal and determine thesynchronization status via a block error rate estimate in the radio linkbased on the channel state information.

FIG. 1 illustrates a communication system 100 including a network 102,base station 104 and user equipment (UE) 106. Various communicationdevices may exchange data or information through the network 102. Thenetwork 102 may be an evolved universal terrestrial radio access(E-UTRA) or other type of telecommunication network. A network entity,such as the base station 104, may assign a UE identifier (UEID) to theUE 106 when the UE 106 first joins the network 102. For one embodiment,the base station 104 may be a distributed set of servers in the network.The UE 106 may be one of several types of handheld or mobile devices,such as, a mobile phone, a laptop, or a personal digital assistant(PDA). In one embodiment, the UE 106 may be a WiFi® capable device, aWiMax® capable device, or other wireless devices.

FIG. 2 illustrates a possible configuration of a computing system to actas a base station 104. The base station 104 may include acontroller/processor 210, a memory 220, a database interface 230, atransceiver 240, input/output (I/O) device interface 250, and a networkinterface 260, connected through bus 270. The base station 104 mayimplement any operating system, such as Microsoft Windows®, UNIX, orLINUX, for example. Client and server software may be written in anyprogramming language, such as C, C++, Java or Visual Basic, for example.The server software may run on an application framework, such as, forexample, a Java® server or .NET® framework.

In FIG. 2, the controller/processor 210 may be any programmableprocessor. The subject of the disclosure may also be implemented on ageneral-purpose or a special purpose computer, a programmedmicroprocessor or microcontroller, peripheral integrated circuitelements, an application-specific integrated circuit or other integratedcircuits, hardware/electronic logic circuits, such as a discrete elementcircuit, a programmable logic device, such as a programmable logicarray, field programmable gate-array, or the like. In general, anydevice or devices capable of implementing the decision support method asdescribed herein may be used to implement the decision support systemfunctions of this invention.

In FIG. 2, the memory 220 may include volatile and nonvolatile datastorage, including one or more electrical, magnetic or optical memoriessuch as a random access memory (RAM), cache, hard drive, or other memorydevice. The memory may have a cache to speed access to specific data.The memory 220 may also be connected to a compact disc-read only memory(CD-ROM), digital video disc-read only memory (DVD-ROM), DVD read writeinput, tape drive, or other removable memory device that allows mediacontent to be directly uploaded into the system.

Data may be stored in the memory or in a separate database. In FIG. 2,the database interface 230 may be used by the controller/processor 210to access the database. The database may contain any formatting data toconnect the UE 106 to the network 102. The transceiver 240 may create adata connection with the UE. The transceiver may create a physicaldownlink control channel (PDCCH) and a physical uplink control channel(PUCCH) between the base station 104 and the UE 106.

The I/O device interface 250 may be connected to one or more inputdevices that may include a keyboard, mouse, pen-operated touch screen ormonitor, voice-recognition device, or any other device that acceptsinput. The I/O device interface 250 may also be connected to one or moreoutput devices, such as a monitor, printer, disk drive, speakers, or anyother device provided to output data. The I/O device interface 250 mayreceive a data task or connection criteria from a network administrator.

The network connection interface 260 may be connected to a communicationdevice, modem, network interface card, a transceiver, or any otherdevice capable of transmitting and receiving signals from the network106. The network connection interface 260 may be used to connect aclient device to a network. The network connection interface 260 may beused to connect the teleconference device to the network connecting theuser to other users in the teleconference. The components of the basestation 104 may be connected via an electrical bus 270, for example, orlinked wirelessly.

Client software and databases may be accessed by thecontroller/processor 210 from memory 220, and may include, for example,database applications, word processing applications, as well ascomponents that embody the decision support functionality of the presentinvention. The base station 104 may implement any operating system, suchas Microsoft Windows®, LINUX, or UNIX, for example. Client and serversoftware may be written in any programming language, such as C, C++,Java or Visual Basic, for example. Although not required, the inventionis described, at least in part, in the general context ofcomputer-executable instructions, such as program modules, beingexecuted by the electronic device, such as a general purpose computer.Generally, program modules include routine programs, objects,components, data structures, etc. that perform particular tasks orimplement particular abstract data types. Moreover, those skilled in theart will appreciate that other embodiments of the invention may bepracticed in network computing environments with many types of computersystem configurations, including personal computers, hand-held devices,multi-processor systems, microprocessor-based or programmable consumerelectronics, network PCs, minicomputers, mainframe computers, and thelike.

FIG. 3 illustrates in a block diagram one embodiment of atelecommunication apparatus or electronic device to act as the UE 106.The UE 106 may be capable of accessing the information or data stored inthe network 102. For some embodiments of the disclosure, the UE 106 mayalso support one or more applications for performing variouscommunications with the network 102. The UE 106 may be a handhelddevice, such as, a mobile phone, a laptop, or a personal digitalassistant (PDA). For some embodiments, the UE 106 may be WiFi® capabledevice, which may be used to access the network 102 for data or by voiceusing VOIP.

The UE 106 may include a transceiver 302, which is capable of sendingand receiving data over the network 102. The UE 106 may include aprocessor 304 that executes stored programs. The UE 106 may also includea volatile memory 306 and a non-volatile memory 308 which are used bythe processor 304. The UE 106 may include a user input interface 310that may comprise elements such as a keypad, display, touch screen, andthe like. The UE 106 may also include a user output device that maycomprise a display screen and an audio interface 312 that may compriseelements such as a microphone, earphone, and speaker. The UE 106 alsomay include a component interface 314 to which additional elements maybe attached, for example, a universal serial bus (USB) interface.Finally, the UE 106 may include a power supply 316.

A UE 106 may determine whether a radio link is in synchronization or outof synchronization with a base station by assuming the transmission of acontrol channel type with a specific format, subcarrier mapping,transmit antenna configuration, and power boost. The transmission formatmay correspond to a particular error correcting code type (e.g., aconvolutional code, block code, turbo-code), payload size, code rate,block size, modulation type, or other error correcting code type. Thecontrol channel type need not be physically transmitted in the signal,and no actual decoding followed by cyclical redundancy check (CRC) maybe necessary to detect whether the radio link isout-of-synchronization/in-synchronization. The UE 106 may make thedetection by using an estimate of the channel state for a portion of thesub-frame which contains the control channel, such as propagationchannel coefficients, interference variance, among other channelinformation. The channel state information may be estimated fromcell-specific reference signals or by other methods. The channel statemay be defined in generic terms as the realization of the propagationchannel between the transmitter and the receiver together with noise andinterfering signals over the time-frequency region of signal reception.As one example, channel state may refer to the collection of theper-subcarrier channel coefficients and the per-subcarrier interferenceplus noise variance statistics. As another example, channel stateinformation may refer to the per-subcarrier signal to interference andnoise ratio (SINR).

The UE 106 may estimate the block error rate (BLER) of a radio link todetermine if the link is usable, in failure, or in recovery. The SINR ofthe reference signal computed over the entire time-frequency resourcesin the control region may be used as an input to a channel statefunction describing channel state information. The channel stateinformation function may map the sub-band signal-to-noise ratio (SNR)and channel quality information (CQI) type metrics. In one particularimplementation, the sub-carrier level SNR is mapped to block error rate(BLER). The channel state information function may approximate referencesignal SINR computed over those resource element groups corresponding tothe physical downlink control channel (PDCCH) codeword. The channelstate information function may be a cascaded set of functions. In oneembodiment, a first sub-function may take the received signal as aninput to calculate an estimate of the channel state, such as a channelcoefficient estimated per subcarrier and the interference and noisevariance per sub-carrier. A second sub-function may take the channelstate estimate and map that to the BLER estimate.

Different UE receiver implementations may have different PDCCHdemodulator or decoder capabilities. The BLER mappings for a UE 106 maybe adjusted to more accurately reflect the actual implementation.Alternately, a UE 106 may use pre-specified functions to obtain an“effective SINR” metric and for comparison against thresholds toidentify an out-of-synchronization or in-synchronization event.Alternatively, a UE 106 may form mean mutual information per bit (MMIB)estimates or channel capacity estimates instead of BLER to determinewhether the link can support reliable transmissions of PDCCH.

Typically, a radio link monitoring mechanism (implemented in software orhardware or a combination of the two) includes determining whether anout-of-synchronization event or an in-synchronization event has occurredby processing the received signal over an evaluation window. Thedetected out-of-synchronization or in-synchronization events can befurther processed. For example, indications corresponding to eitherevent (out-of-synchronization or in-synchronization) can be filteredover a period of time to declare a link failure event or a link recoveryevent.

Suppose for example, that the transmission includes PDCCH codewords andthe receiver attempts to decode them. If the receiver is able todetermine whether the control codewords were decoded correctly, then itcan make use of this information in addition to the channel stateinformation to determine an out-of-synchronization or anin-synchronization event has occurred. If one control codeword or aplurality of control codewords that were received within an interval oftime were decoded correctly, then the receiver may not choose to processthe out of synchronization indications. Alternately, if one controlcodeword or a plurality of control codewords that were received withinan interval of time were decoded correctly, the receiver may choose togenerate and process an in synchronization indication. On the otherhand, if the receiver had the mechanism to determine that one or more ofthe control codewords intended for the receiver, were decodedincorrectly, it may choose not to generate and process insynchronization indications.

In one embodiment, the controller is configured to determine asynchronization based on a mapping of channel state information todecoder error rate corresponding to a hypothetical control code word.The controller is also configured to attempt to decode a controlcodeword in a received signal and to conclude that an out ofsynchronization event has not occurred if the control codeword isdecoded successfully regardless of an indication of the mapping. In someimplementations, the controller is configured to conclude that an insynchronization event has occurred if the control codeword is decodedsuccessfully regardless of an indication of the mapping. The controllermay also be configured to conclude that an in synchronization event hasnot occurred if at least one control codeword addressed to the UE wasdecoded unsuccessfully.

The indications generated for out of synchronization events and insynchronization events are respectively processed further. Theindications can be filtered for an evaluation period. A receiver can beconfigured to operate either in discontinuous reception (DRX) modecomprising period on and sleep durations or in non-DRX mode. The DRX andnon-DRX modes can have different evaluation time periods for theindications. Further, the evaluation time period for the indications forDRX mode can be dependent on the DRX cycle periodicity. The receivertransitions from one mode to another. In FIG. 7, for example, a receiveroperating in DRX mode transitions to non-DRX mode. In FIG. 8, a receiveroperating in DRX mode with one periodicity transitions to a DRX modehaving another periodicity, which may be greater or less than that ofthe first DRX mode.

Suppose that the receiver mode of operation prior to the transition hasa first filter with a first period of evaluation for the indications.And the second receiver mode of operation after the transition has asecond filter with a second period of evaluation for the indications.There are two options that the receiver has for continuing theevaluations immediately after the transition. In one embodiment, thereceiver uses a first filter with a first period of evaluation from thestart of the transition up until a time equal to the second period ofevaluation corresponding to the second filter has elapsed. Subsequent tothat, it can start using the second filter with the second period ofevaluation. More particularly, the controller coupled to thetransceiver, is configured to estimate block error rate for ahypothetical control codeword. The controller is also configured todetermine radio link synchronization when the UE is in a first mode ofoperation using a first filter output based on the estimated block errorrate and to determine radio link synchronization when the UE is in asecond mode of operation using a second filter output based on theestimated block error rate. Upon transitioning from the first mode ofoperation to the second mode of operation, the controller is configuredto initially use the first filter output for determining radio linksynchronization and then to use the second filter output for determiningradio link synchronization while operating in the second mode ofoperation.

In one embodiment, the first mode of operation is discontinuousreception mode and the second mode of operation is non-discontinuousreception mode. In one implementation of this embodiment, the controlleris configured to use the first filter output for determining radio linksynchronization from the start of the transition to the state ofnon-discontinuous reception mode until a time equal to a secondevaluation interval of the second filter has elapsed. In otherimplementations, the first filter output may be used for other timeperiods.

In another embodiment, the first mode of operation is a firstdiscontinuous reception mode and the second mode of operation is asecond discontinuous reception mode, a periodicity of the firstdiscontinuous reception mode is different than a periodicity of thesecond discontinuous reception mode. In one implementation of thisembodiment, the controller configured to use the first filter output fordetermining radio link synchronization from the start of the transitionto the state of the second discontinuous reception mode until a timeequal to a second evaluation interval of the second filter has elapsed.In other implementations, the first filter output may be used for othertime periods.

In another embodiment, the receiver can cease to perform evaluation orthe indicators generated from the start of the transition up until atime equal to the second period of evaluation corresponding to thesecond filter has elapsed. Subsequent to that, it can start using thesecond filter with the second period of evaluation. More particularly,the controller coupled to the transceiver, is configured to a estimateblock error rate for a hypothetical control codeword. The controller isalso configured to determine radio link synchronization when operatingin a first mode of operation using a first filter output based on theestimated block error rate. Upon transitioning from the first mode ofoperation to a second mode of operation, the controller is configured tonot determine radio link synchronization for an initial period and thento determine radio link synchronization when operating in the secondmode of operation using a second filter output based on the estimatedblock error rate.

In one embodiment, the first mode of operation is discontinuousreception mode and the second mode of operation is non-discontinuousreception mode. In one implementation of this embodiment, the controlleris configured to not evaluate radio link synchronization from the startof transitioning to the second mode of operation for an initial periodcorresponding to a time equal to a second evaluation interval of thesecond filter. In other implementations, other initial time periods maybe used.

In another embodiment, the first mode of operation is a firstdiscontinuous reception mode and the second mode of operation is asecond discontinuous reception mode, a periodicity of the firstdiscontinuous reception mode is different than a periodicity of thesecond discontinuous reception mode. In one implementation of thisembodiment, the controller is configured to not evaluate radio linksynchronization from the start of transitioning to the second mode ofoperation for an initial period until a time equal to a secondevaluation interval of the second filter has elapsed. In otherimplementations, other initial time periods may be used.

The channel state information or BLER estimate may be obtained from eachsub-frame sampled from the processing window in continuous receptionmode. For a discontinuous reception mode of operation, these sub-framesmay correspond to the sub-frames, or a subset thereof, at the pagingoccasions successively separated by a discontinuous cycle period. Theprocessing windows may correspond to multiple discontinuous receptionperiod durations from which the sub-frames are sampled.

The UE 106 may use the aggregated per-sub-band channel state informationfor the PDCCH codeword to obtain the BLER estimate. Since the actualtime-frequency diversity experienced by the PDCCH codeword in thepropagation channel generates the BLER estimate, the estimate of BLERmay be more accurate. On the other hand, if the UE 106 uses a singlereference signal SINR level, compared against thresholds, fordetermination of the synchronization events, the wideband nature of thePDCCH codeword mapping and the associated gains due to frequencydiversity for higher bandwidths, such as greater than 1.4 MHz, may notbe captured. A synchronization event may be an event in which thesynchronization status of the radio link changes. This practice may leadto increased false triggers of out-of-synchronization events when thenarrowband reference signal SINR is low, such as when signal over themeasurement bandwidth is in fade, while the PDCCH codeword would havebeen decodable.

FIG. 4 illustrates a method 400 for determining a synchronization event.At 402, the UE maintains a radio link with a base station. At 404, theUE may monitor the synchronization status associated with the radiolink. At 406, the UE maps channel state information to a synchronizationstatus of the radio link based on the received signal over a specifiedbandwidth. At 408, the UE determines the synchronization status via theBLER estimate in the radio link based on the channel state information.At 410, the UE determines the synchronization event based upon the BLER.

The UE 106 may use different formats to determine when anout-of-synchronization event has occurred versus when anin-synchronization event has occurred. A first threshold, hereinreferred to as a failure threshold, may signify at which point a BLERbecomes high enough to indicate that a radio link has become out ofsynchronization. A second threshold, herein referred to as a recoverythreshold, may signify at which point a BLER becomes low enough toindicate that a radio link has become in synchronization. Both levelsmay be determined as a function of bandwidth, such as 1.4, 3, 5, 10, 15,20 MHz, and transmit antenna configuration, such as 1×2, 2×2 spacefrequency block coding (SFBC) or 4×2 SFBC-frequency switchingtransmission diversity (FSTD). Alternately, the UE 106 may use just twolevels, one for out-of-synchronization and one for in-synchronization,common across bandwidths and transmit antenna configuration.

An out-of-synchronization event may occur when the SNR drops or thechannel quality deteriorates such that the control or shared channelsbecome un-decodable. The threshold may be determined by considering thebest coverage available when the maximum error protection, maximum powerboosting and maximum frequency-time diversity transmission are deployed.

The UE 106 may use reference signal symbols to obtain a per-sub-bandchannel state information for the control region of a sub-frame. Asub-band may be one control channel element (CCE), resource elementgroup, or some other aggregation of subcarriers that contain the mappedsymbols of the PDCCH codeword. A PDCCH payload may have a specificformat, such as Format 1A. The format may have a specific minimumpayload size, such as 31 bits for 10 MHz; a specific maximum aggregationlevel applicable to the bandwidth, such as an aggregation level of 8 for10 MHz bandwidth; and a specific codeword-to-subcarrier mapping thatachieves the maximum time-frequency diversity. Alternately, the UE 106may use a typical payload size, typical aggregation level, and a typicalcodeword to subcarrier mapping. The UE 106 may use a maximum power boostrelative to the reference signal, such as +3 dB, or a typical powerboost relative to the reference signal, such as 0 dB.

The base station 104 need not actually transmit the PDCCH payload of theassumed type. The UE 106 may calculate the per-sub-band channel stateinformation for the subcarrier under the assumption that PDCCH payloadof the assumed type was transmitted. The UE 106 may use the per-sub-bandchannel state information for the entire PDCCH codeword for the assumedtype to obtain a BLER estimate for the PDCCH codeword. The UE 106 mayobtain the BLER estimate for each of the sub-frames in anout-of-synchronization processing interval, such as an interval of 200ms. The UE 106 may average these estimates over theout-of-synchronization processing duration.

To generalize this mapping, the UE 106 may define channel stateinformation that maps all the per-sub-band SINR or CQI-type metrics fromthe sub-frames to a single BLER estimate that is compared against athreshold for determination of the out-of-synchronization event. The UE106 may define a criterion for out-of-synchronization detection as anevent in which the average BLER estimate is greater than a setpercentage over the out-of-synchronization processing duration or theBLER estimate is greater than a set percentage for the last set numberof sub-frames.

In one example, the UE 106 may form BLER estimates for five sub-framesseparated by 40 ms in a 200 ms processing window for the purpose ofout-of-synchronization evaluation. For a sub-frame for which the PDCCHBLER is being estimated, the UE 106 may assume that a PDCCH Format 1Apayload of ˜42 bits (for 10 MHz operation) is being transmitted in thecontrol region on the first n (0<n<4) orthogonal frequency divisionmultiplexing (OFDM) symbols in the sub-frame, starting the first CCE inthe common search space at an aggregation level of 8. The UE 106 mayidentify the time-frequency resource element groups on which thecodeword gets mapped and calculates the reference signal SINR for thoseresource element groups. The reference signal SINR may be calculated bysignal interpolation, by a minimum mean square error channel and noiseestimator, or some other technique. For 72 resource element groups, theUE 106 may use 72 non-negative reference signal SINR terms in BLERestimation. The UE 106 may use the reference signal resources from thesame sub-frame for reference signal SINR estimation for the controlresource element groups, as well as current, past and future sub-frames.The channel state information that maps all the reference signal-SINRterms to a BLER value may be determined off-line and pre-stored in theUE 106. This function may map the 72 reference signal SINR terms to aBLER estimate value for the Format 1A PDCCH codeword. One example ofchannel state information may be a function that takes mean referencesignal SINR and the covariance of a reference signal SINR, capturing themean level and the time-frequency variation of the reference signalSINR, as input arguments and outputs a BLER value. The power boost valueassumed for the Format 1A PDCCH payload may be subsumed into the channelstate information. Alternately, the power boost may be added to thereference signal SINR terms to reflect the SINR corresponding to theresource element groups to which the PDCCH payload is mapped. The BLERestimates from the 5 sub-frames may then be averaged to compute anaverage BLER which is compared against a threshold, such as 10%, tocheck if the out-of-synchronization criterion is satisfied.

Out-of-synchronization determination may create a processing overheadrelative to the case when the out-of-synchronization event is determinedusing, for example, the narrowband reference signal SINR measure. Tocorrect for this, the UE 106 may subdivide the out-of-synchronizationprocessing window of into two parts. The UE 106 may continuously monitorthe narrowband reference signal received power (RSRP) averaged over theduration of the first part. Since the narrowband reference signal SINRmeasure somewhat correlates with the wideband CQI-type metric orper-sub-band SINR for the PDCCH resource elements, a synchronizationcheck threshold may be used to trigger BLER estimation. For example, ifthe narrowband reference signal SINR drops below the synchronizationthreshold chosen by the implementation by averaging reference signalSINR over the first part of the processing window, the second part mayuse the synchronization threshold to trigger the search for anout-of-synchronization event using the BLER mapping approach.

FIG. 5 illustrates a method 500 for determining whether a radio link isout of synchronization. At 502, the UE maintains a radio link with abase station. At 504, if the RSRP is less than a synchronization checkthreshold, the UE may map channel state information for the radio linkbased on the received signal over a specified bandwidth (Block 506). At508, the UE sets the failure range based upon a payload parameter, suchas a control channel type. The control channel type may be a specifictransmission format, sub-carrier mapping, transmit antennaconfiguration, power boost, or other parameters. The transmission formatmay be an error correcting code type, payload size, code rate, blocksize, modulation type, or other formats. The error correcting code typemay be a convolution code, block code, turbo-code, or other codes. Atblock 510, the UE estimates a metric for the radio link based on thechannel state information using a format best suited for determining ifthe radio link failure is about to occur, or failure format. The metricmay be a block error rate, a mean mutual information per bit, averagesignal to noise ratio, channel capacity, or other metric. If the metricis within the failure range, at 512, the UE may designate the radio linkas having an out of synchronization event (Block 514).

The UE 106 may use a different format for determining anin-synchronization event, with less overhead. The UE 106 may usereference signal symbols to obtain a per-sub-band channel stateinformation for the control region of a sub-frame. A sub-band may be onecontrol channel element (CCE), resource element group, or some otheraggregation of subcarriers that contain the mapped symbols of the PDCCHcodeword. A PDCCH payload may have a specific format, such as Format 1Aor 1C. The format may have a specific maximum payload size, such as 31bits for 10 MHz; a specific minimum aggregation level applicable to thebandwidth, such as an aggregation level of 2; and a specificcodeword-to-subcarrier mapping that achieves the minimum time-frequencydiversity. Alternately, the UE 106 may use a typical payload size,typical aggregation level, and a typical codeword to subcarrier mapping.The UE 106 may use a minimum power boost relative to the referencesignal, such as −6 dB, or a typical power boost relative to thereference signal, such as 0 dB.

The base station 104 need not actually transmit the PDCCH payload of theassumed type. The UE 106 may calculate the per-sub-band channel stateinformation for the subcarrier under the assumption that PDCCH payloadof the assumed type was transmitted. The UE 106 may use the per-sub-bandchannel state information for the entire PDCCH codeword for the assumedtype to obtain a BLER estimate for the PDCCH codeword. The UE 106 mayobtain the BLER estimate for each of the sub-frames in anin-synchronization processing interval, such as an interval of 100 ms.The UE 106 may average these estimates over the in-synchronizationprocessing duration.

To generalize this mapping, the UE 106 may define channel stateinformation that maps all the per-sub-band SINR or channel stateinformation-type metrics from the sub-frames to a single BLER estimatethat is compared against a threshold for determination of thein-synchronization event. The UE 106 may define a criterion forin-synchronization detection as an event in which the average BLERestimate is less than a set percentage over the in-synchronizationprocessing duration or the BLER estimate is less than a set percentagefor the last set number of sub-frames.

For in-synchronization evaluation, the UE 106 may use Format 1C, as thesystem information block (SIB), paging channel (PCH) and random accesschannel (RACH) response messages are addressed by this PDCCH format.After the UE 106 goes to in-synchronization state, the UE 106 mayattempt cell reselection and send a RACH message on the uplink. Thesignal conditions may be such that the RACH response and the SIBtransmissions are decodable by the UE 106. Further, a Format 1C codewordmay have lower error protection, minimum power boost, and subcarriermapping that achieves minimum frequency-time diversity resulting in thelimiting behavior. Alternately, the UE 106 may use any other typicalcontrol channel format aimed at characterizing the typical behavior.

In one example, the UE 106 may form BLER estimates for five sub-framesseparated by 20 ms in a 100 ms processing window for the purpose ofin-synchronization evaluation. For a sub-frame for which the PDCCH BLERis being estimated, the UE 106 may assume that a PDCCH Format 1C payloadof ˜31 bits (for 10 MHz operation) is being transmitted in the controlregion on the first three OFDM symbols in the sub-frame, starting thefirst CCE in the common search space at an aggregation level of 2. TheUE 106 may identify the time-frequency resource element groups on whichthe codeword gets mapped and calculate the reference signal SINR forthose resource element groups. The UE 106 may use channel stateinformation to determine the BLER for that sub-frame.

FIG. 6 illustrates a method 600 of determining whether a radio link isin synchronization. At 602, the UE maintains a radio link with a basestation. At 604, the UE maps channel state information function for theradio link based on the subcarrier over a specified bandwidth. At 606,the UE sets the recovery range based upon a payload parameter, such ascontrol channel type. The control channel type may be a specifictransmission format, sub-carrier mapping, transmit antennaconfiguration, power boost, or other parameters. The transmission formatmay be an error correcting code type, payload size, code rate, blocksize, modulation type, or other formats. The error correcting code typemay be a convolution code, block code, turbo-code, or other codes. TheUE 106 may estimate the metric for the radio link based on the channelstate information using a format best suited for determining if theradio link recovery is about to occur, or recovery format (Block 608).The metric may be a block error rate, mean mutual information per bit,average signal to noise ratio, channel capacity, or other metric. If themetric is within the recovery range at 610, the UE designates the radiolink as having an in synchronization event (Block 612).

Embodiments within the scope of the present invention may also includecomputer-readable media for carrying or having computer-executableinstructions or data structures stored thereon. Such computer-readablemedia can be any available media that can be accessed by a generalpurpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to carryor store desired program code means in the form of computer-executableinstructions or data structures. When information is transferred orprovided over a network or another communications connection (eitherhardwired, wireless, or combination thereof) to a computer, the computerproperly views the connection as a computer-readable medium. Thus, anysuch connection is properly termed a computer-readable medium.Combinations of the above should also be included within the scope ofthe computer-readable media.

Embodiments may also be practiced in distributed computing environmentswhere tasks are performed by local and remote processing devices thatare linked (either by hardwired links, wireless links, or by acombination thereof) through a communications network.

Computer-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions. Computer-executable instructions also includeprogram modules that are executed by computers in stand-alone or networkenvironments. Generally, program modules include routines, programs,objects, components, and data structures, etc. that perform particulartasks or implement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of the program code means for executing steps of the methodsdisclosed herein. The particular sequence of such executableinstructions or associated data structures represents examples ofcorresponding acts for implementing the functions described in suchsteps.

While the present disclosure and the best modes thereof have beendescribed in a manner establishing possession by the inventors andenabling those of ordinary skill to make and use the same, it will beunderstood that there are equivalents to the exemplary embodimentsdisclosed herein and that modifications and variations may be madethereto without departing from the scope and spirit of the inventions,which are to be limited not by the exemplary embodiments but by theappended claims.

What is claimed is:
 1. A wireless communication terminal comprising: atransceiver configured to operate in either discontinuous reception(DRX) mode or in non-DRX mode; and a controller coupled to thetransceiver, the controller configured to determine a synchronizationbased on determining a decoder error rate corresponding to ahypothetical control codeword over an evaluation period that includes atleast one of a first evaluation period and a second evaluation period,wherein the transceiver uses the first evaluation period when thetransceiver is configured to operate in DRX mode and the secondevaluation period when the transceiver is configured to operate innon-DRX mode, wherein the first evaluation period is different than thesecond evaluation period, the controller configured to attempt to decodea control codeword in a received signal based on the hypotheticalcontrol codeword, the controller configured to conclude that an out ofsynchronization event has not occurred if the control codeword isdecoded successfully.
 2. The terminal of claim 1 wherein the controlleris configured to conclude that an in synchronization event has occurredif the control codeword is decoded successfully.
 3. The terminal ofclaim 1 wherein the controller is configured to conclude that an insynchronization event has not occurred if at least one control codewordaddressed to the terminal was decoded unsuccessfully.
 4. The terminal ofclaim 1 wherein the controller is configured to: receive a referencesignal transmitted from a base station; and determine the decoder errorrate corresponding to the hypothetical control codeword based on thereceived reference signal and a payload parameter of the hypotheticalcontrol codeword.
 5. The terminal of claim 1 wherein the controller isconfigured to determine a synchronization status from the decoder errorrate.
 6. The terminal of claim 1 wherein the controller is configured toset a recovery range based upon at least one payload parameter.
 7. Theterminal of claim 1 wherein the controller is configured to: receive areference signal transmitted from a base station; and determine asynchronization status based on the received reference signal.
 8. Theterminal of claim 1 wherein the hypothetical control codeword is one ofa downlink control information Format 1A and a downlink controlinformation Format 1C.
 9. The terminal of claim 1 wherein the controlleris configured to determine that the decoder error rate is larger than afirst threshold.
 10. The terminal of claim 1 wherein: the controller isconfigured to conclude that the out of synchronization event hasoccurred if at least one control codeword is decoded unsuccessfully. 11.The terminal of claim 1 wherein the evaluation period is comprised ofthe first evaluation period followed by the second evaluation period.12. The terminal of claim 1 wherein the evaluation period is comprisedof only the first evaluation period.
 13. The terminal of claim 1 whereinthe evaluation period is comprised of only the second evaluation period.14. A wireless communication terminal comprising: a transceiverconfigured to operate in a first discontinuous reception (DRX) mode orin a second DRX mode; and a controller coupled to the transceiver, thecontroller configured to determine a synchronization based ondetermining a decoder error rate corresponding to a hypothetical controlcodeword over an evaluation period that includes at least one of a firstevaluation period and a second evaluation period, wherein thetransceiver uses the first evaluation period when the transceiver isconfigured to operate in the first DRX mode and the second evaluationperiod when the transceiver is configured to operate in the second DRXmode, wherein the first evaluation period is different than the secondevaluation period, the controller configured to attempt to decode acontrol codeword in a received signal based on the hypothetical controlcodeword, the controller configured to conclude that an out ofsynchronization event has not occurred if the control codeword isdecoded successfully.
 15. The terminal of claim 14 wherein a periodicityof the first DRX mode is different than a periodicity of the second DRXmode.
 16. The terminal of claim 14 wherein the evaluation period iscomprised of only the second evaluation period.